This research proposal is designed to investigate the molecular basis of estrogens and retinoids in the regulation of uterine proliferation. Aim 1 is to identify the RAR signaling pathways that mediate the effect of retinoids on estrogen-induced uterine proliferation, i.e. RAR/RAR, RAR/RXR, or RXR/RXR dimers, as well as RXR/other protein hetero-dimers. Aim 2 is to determine the role of endogenous retinoids in the regulation of estrogen-induced uterine proliferation. Aim 3 is to identify the molecular mechanisms involved in the effects of retinoids on estrogen-regulated gene expression in the uterus.